The present invention relates to permanent magnet rotors, and more particularly to a device and method for retaining the rotor core and the magnetic elements in a secure assembled relation.
Permanent magnet rotors are frequently used in dynamo electric machines such as motors and generators. A typical permanent magnet rotor includes a number of magnets secured to the outer periphery of a rotor core. In recent years, numerous designs of permanent magnet rotors have been proposed since improvements have been made in the quality of the magnets.
Retention of the magnets in predetermined rotational positions about the rotor core is critical to the good functioning of the motor. The attachment of the magnets needs to be strong enough to withstand the centrifugal forces due to the high speed rotation of the rotor or to withstand the angular forces due to unexpected changes in the angular velocity of the rotor. It is imperative to prevent the magnets from moving either axially or radially. If axial movement is allowed, one or more magnets may not properly align with the rotor core and the rotor efficiency will diminish. If radial movement occurs, the physical contact between the rotor and the stator will result in damage to the rotor.
The prior art illustrates a number of methods and techniques for retaining magnets in fixed relation on the rotor core. One way of preventing the movement of the magnets relative to their core in permanent magnet rotors is to install spacers between adjacent magnets. Another way of preventing the movement of the magnet is to cover the area with a binder made of a synthetic material to fill the voids between the magnets and the core. This technique provides a more rigid structure compared to the use of magnets alone, which prevents the magnet movement about the core during motor operation.
A popular way of securing the magnets to the core according to the prior art is to use a tubular sleeve to enclose and hold the magnet segments in place. The sleeve prevents radially outward movement due to centrifugal force and also against axial movement. Furthermore, the prior art also considered heat shrinking the sleeve over the magnets.
FIG. 1 illustrates a sectional front view of a conventional permanent magnet rotor. The Figure illustrates a conventional permanent magnet rotor 10 comprising a core 20, a tubular sleeve 30, a pair of identical configured end plates 40, and magnets 60.
While many of the prior art approaches to retaining magnets on the core have been found satisfactory for their intended applications, many of them fail to adequately retain the magnets in fixed rotational position on the core during high speed operation.
For example, the shrink fit is inadequate to maintain the magnet/spacers or end plates in place during high speed operations. Furthermore, the sleeve fails to retain the end plates in a fixed position on the rotors during high speed operation resulting in dislocation of the end plates. This dislocation will generate high imbalance and results in catastrophic consequences for the rotor.
As can be seen, there is a need for a rotor configuration wherein the magnet segments are contained or fixed in position on the rotor core, especially during high speed operating conditions. Such a configuration should be simple in design and relatively low cost in its manufacture.